MG Midget and Sprite Technical I'm doing it: 1275 to 1500 conversion BBS discussion at MG-Cars.net

MG Midget and Sprite Technical - I'm doing it: 1275 to 1500 conversion

Why, you may ask. Oh God, why? Yes, the road ahead is dark my friends, a midget Black Hole, if you will. Two cars will be fused, many resources will be squandered, sparks will fly and fumes will waft, but a road worthy machine will, will I say, rise from the surgeon's slab. Awkward at first yes, yes, but driven, if you will, towards a higher purpose, that loftiest of ambitions OH! to seize the chalice, and drink in the unsanctioned ambrosia of 63 mph @ 2,000 rpm! Seriously, I've grown bored with my '79 1500, but it has a rebuilt Spitfire engine (non-ported head) mated to the Frontline Ford type nine 5-speed kit, both with under 4,000 miles on them. I've been looking for a body to put said engine/gearbox in for a few years, finally found the right car at the right price. As mentioned above, my 1500 does 63 mph on the highway at 2,000 rpm. I don't know how fast she'll go 'cause I'm chicken/sane but I'd guess 115 mph isn't out of the question. In short, too sweet (and expensive) a package to abandon, so into the 1967 Mark 3 she goes. 1500's rear axle as well. The transplantee is a February (or thereabouts) 1967 build, negative earth but with the simpler wiring harness that disappeared not long after, no body cancer, just worn out paint from being in the sun and fog too long. This thread will fall off the bottom of the Technical page soon enough, but I will refresh it on occasion, with pictures, as progress is made. There is a dearth of information on the interwebs about this particular surgical abomination, I intend on adding to the knowledge base by sharing my project. Wish me luck. And in homage to those who have gone before and their wildly out-of-the-box ideas, their possibly slippery grip on the concept of beginnings, middles and ends, and their endlessly optimistic spirit, I leave you with an oldie but a goodie: Prop's Flow Chart.

Richard Reeves

Okay first things first: In my OP I reported this to be a negative earth vehicle. Nyet. Positive earth, 1967, partially converted to negative earth by a prior owner. I say partial because wiper motor terminals not reversed, haven't got a close-up look at the fuel pump wiring yet. anamnesis, I said bored, but offended would have been more accurate. My 1979 California car (known henceforth as Donormobile) is so dumbed down with safety and worse, emission control "features" as to be a mockery of the original design and intent. Under the bonnet it's a Medusa's Nightmare. I crave the simplicity of a simpler time, a simpler machine. As to debumpering instead, well, let's just say that I get my pets debumpered, which keeps them compliant, predictable, docile and boring. Just like Donormobile.. Progress update: I've been working an ancillaries and cosmetics, haven't yet pulled the lump from Donormobile, which is really going to be necessary to get a proper look at the geometry of the coming surgeries. In the first pic multiple things visible: Blue: repositioned coil and solenoid Green: new clutch master to slave fluid line Upcoming surgical procedures: 1: The inner leftside footwell wall needs to be opened to accommodate the starter motor/flywheel assembly. 2. This brace (and old coil mount) likely needs removal to accommodate the twin HS4 set going in. 3. Exhaust downpipe location will need widening to accommodate the twin pipes of the 4-2-1 header unit. 4. Not visible, the tunnel crossmember needs removal and replacement. Numbers 1 thru 3 are easy, this is somewhat more complex. I've already done it on Donormobile so hopefully some muscle memory kicks in. 5. 5A & 5B are the big Kahunas: 5A in the 1500 series is deeply concave to accommodate both the crankshaft pulley and the oil pan. 5B appears to not exist on the 1500, again, to accommodate the crankshaft pulley. Although this piece appears to be structurally quite important to my untrained eye, it's complete absence in the 1500 gives one pause to consider various options. Second pic: I've pulled and installed the accelerator pedal pivot rod from Donormobile, as the required tunnel mod likely would have fouled the original pedal operation. Old and new mounting points circled in red. The inset pic gives a decent view of the bulge in the 1500 tunnel that I have to replicate. Lastly, although not strictly relevant to the thread title, the keen observer may have noticed a few more wires than typical for the vintage: there's a dynamo-to-alternator conversion afoot, plus I'm adding a gauge or two and an indicator lamp or two, I wanted all that incorporated into the new harness from the get-go.

Richard Reeves

Valuable information Rob thank you. Those chamfers sound subtle enough to miss, glad I know about them. Google AI reports my 1500 lump and Ford type 9 combo weigh in at ~34# net increase over an A-series/ribcase combo. While I don't exactly trust AI to get it right, if this is anywhere near correct it seems sufficiently minimal to not require attention/compensation. I suppose I should weigh the lump and box while out of the car. The further back the center of gravity is on that combo the more of that 34# is shared with the rear axle as well. Not much granted, but some. If anyone begs to differ please tell me now while I'm rebuilding the front suspension. By the way, image shows mileage on my project 1967 car as acquired. Inset shows the engine # in Donormobile that's going into the 1967. I'm not much for omens and such, but I think that's an omen. Pretty sure.

Richard Reeves

Me too Bill. And we're not alone. "I've been mad for f*cking years, absolutely years, been over the edge for yonks, been working me buns off for bands..." "I've always been mad, I know I've been mad, like the most of us...very hard to explain why you're mad, even if you're not mad..." ----- So take a breath. Don't catch that wave. Don't race to an early grave. --- https://youtu.be/9YOyDSjXJnk?feature=share

anamnesis

This thread was discussed between 15/06/2025 and 17/07/2025

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